1. Field of the Invention
This invention relates to non-staining room temperature vulcanizable silicone sealants, compositions, and methods to prepare same.
2. Prior Art
Many methods have been proposed to eliminate the problem encountered with the use of room temperature curing silicone sealants in construction of buildings of becoming dirty and of staining the surrounding building materials adjacent to the sealant. This creates an unattractive appearance. Cleaning the dirt off of the sealant and the stain off the adjacent building materials is an expensive method and the results are often unsatisfactory. It is therefore the hope of the construction industry that a silicone sealant be developed which does not itself become dirty or stain the adjacent building materials.
The staining of building materials adjacent to the sealant apparently occurs when materials, such as polyorganosiloxanes migrate to these surfaces from the cured sealant and contaminants from the air or precipitation adhere to these surfaces and they become stained. The aesthetics of the building are reduced. The construction industry is therefore interested in sealants which overcome this problem. Certain surfactants have been proposed to overcome this drawback of the room temperature silicone sealants. Some of these surfactants include the nonionic or anionic surfactants containing polyoxyethylene segment, sorbitan, or disaccharide residual groups in the polyoxyethylene described in an abstract for Japanese Kokai [Laid Open] Patent Publication No. 56-76453 [81-76453], assigned to Toshiba Silicone KK, Jun. 24, 1981; and an abstract for Japanese Kohai [Laid Open] Patent Publication No. 56-76452 [81-76452], assigned to Toshiba Silicone KK, Jun. 24, 1981. These surfactants appear to be effective to reduce the surface dirt pick up but only when large amounts are used. The use of large amounts of these surfactants leads to a decrease in adhesion of sealant to building materials and this is unsatisfactory.
Another solution to the sealant becoming dirty and the surfaces adjacent to the sealant staining, was proposed by Arai in U.S. Pat. No. 4,460,740, issued Jul. 17, 1984. Arai teaches that conventional silicone sealant compositions which contain a limited amount of a specific fluorine-containing surface active agent solves the problem, encountered by cured sealant when used for sealing or caulking of a joint in building structures, of surface staining which eventually spreads over adjacent surfaces. Arai teaches that the fluorine-containing surface active agents can be amphoteric, anionic, cationic, and non-ionic surface active agents. Arai illustrates the amphoteric fluorine-containing surface active agents by the following formulae ##STR2## in which G is a monovalent organic group or preferably, a monovalent hydrocarbon group, A is an alkyl group or a hydroxyalkyl group, l, n, and q are each zero or a positive integer and p is a positive integer. Anionic surface active agents are described as C.sub.p F.sub.(2p+1) SO.sub.3 M or C.sub.p F.sub.(2p+1) COOM, in which M is a hydrogen atom or an alkali metal atom. Cationic surface active agents are illustrated by the formula C.sub.p F.sub.(2p+1) SO.sub.2 NH(CH.sub.2).sub.n N.sup.+ G.sub.3 W.sup.- in which W is a halogen atom and R, n, p are defined above. The non-ionic surface active agents are illustrated by the formula C.sub.p F.sub.(2p+1) SO.sub.2 NG(CH.sub.2 CH.sub.2 O).sub.u H in which u is zero or a positive integer and G and p are described above.
Arai teaches that these particular fluorine-containing surface agents are useful in a silicone sealant composition of from 0.01 to 5.0 parts by weight per 100 parts by weight of the total components where the composition is 100 parts by weight of a diorganopolysiloxane blocked on both molecular chain ends with a hydroxy group directly bonded to silicon atom, 0.1 to 25 parts by weight of an organosilicon compound having at least two hydrolyzable groups per molecule on the average, 1 to 400 parts by weight of a filler, and optionally up to 5.0 parts by weight of a curing catalyst. Such compositions are taught as insusceptible to stain on the surface of a cured rubbery elastomer. Arai teaches that these compositions cure to sealants which begin to show surface stain after outdoors exposure from 1 to 6 months depending upon the particular fluorine-containing surface active agent used. The fluorine-containing surface active agents showing the best results were the amphoteric surface active agents.
Arai, along with Yoshio Inoue and Takeo Inoue (Inoue et al), in U.S. Pat. No. 4,695,603, issued Sep. 22, 1987, teach that long term resistance to stain is not accomplished by sealant compositions containing the fluorine-containing surface active agent as described by Arai in U.S. Pat. No. 4,460,740. Inoue et al teach that in order to obtain surface stain resistance, in addition to the fluorine-containing surface active agent, an organosilicon compound of the following formula is required EQU R.sup.1 --CO--NR.sup.2 --(CH.sub.2).sub.t SiR.sup.3.sub.s O.sub.(3-s)/2
in which R.sup.1, R.sup.2, and R.sup.3 are each a hydrogen atom, a monovalent hydrocarbon group, or a monovalent hydrocarbon group substituted with halogen or cyano, s is zero, 1, 2, or 3, and t is a positive integer not larger than 10. These organosilicon compounds are present in the composition in amounts of from 0.01 to 10 parts by weight. The use of both of the fluorine-containing surface active agent of Arai and the organosilicon compound of Inoue et al show that the onset of stain may begin after 12 months depending upon the particular fluroine-containing surface active agents, the particular organosilicon compound, and their amounts in the sealant composition.
Although the prevention of surface staining and staining of adjacent surfaces of up to 12 months is an advantage, buildings are intended to last for many years and the prevention of sealant surface staining and dirtying and/or staining on building materials adjacent to the cured sealant is desirable for as long as possible. Therefore, an extensive development program was initiated to provide sealants which would maintain clean surfaces on the sealant and which would maintain adjacent building material surfaces clean over years of exposure to atmospheric conditions.